He said: I heard ar-Rida عليه السلام, who mentioned something, then said: You do not need that – this is Abu Ja`far, who I have sat in my seat to assume my position. And he said: We are the Ahl al-Bayt, the young from us inherit from the elder from us, step by step (i.e. of equal measure). (al-Kafi, Volume 1, hadith 824)(sahih) (صحيح)

He said: I entered upon Abu Ja`far the Second عليه السلام and he debated with me in things; then he said to me: O Abu `Ali, uplift [your] doubt; my father had none but me. (al-Kafi, Volume 1, hadith 825)

He said: I said to ar-Rida عليه السلام: We used to ask you before Allah bestowed upon you Abu Ja`far عليه السلام, and you would say, “Allah will bestow upon me a boy” and Allah has bestowed him upon you. Our eyes have acknowledged him. May Allah spare us from seeing your day – but if that were to occur, to whom will it (i.e. the Imamate) go? So with his hand he pointed to Abu Ja`far عليه السلام while he was standing in front of him. So I said: May I be your ransom, this three-year-old son?! So he said: That would be of no harm to him, as `Isa عليه السلام rose by the proof when he was a three-year-old son. (al-Kafi, Volume 1, hadith 832)